Receptor dynamics shape NK cell function

Natural killer (NK) cells are a subset of innate lymphoid cells that target virally infected and malignant cells. An education process ensures that activating receptors promote NK cell activation in response to infected or abnormal cells and that inhibitory receptors prevent inappropriate NK cell activation by healthy cells. Cells that lack inhibitory receptors are hyporesponsive. Staaf et al. found that the activating receptor NKp46 and the inhibitory receptor Ly49A exhibited dynamic movements in the plasma membrane that differed between educated and hyporesponsive NK cells. Although both receptors were generally restricted to membrane microdomains, NKp46 molecules spent less time in an individual microdomain and diffused faster on educated cells compared to hyporesponsive cells. Conversely, Ly49A molecules were overall more constrained and diffused more slowly on educated cells. Interfering with receptor dynamics reduced signaling by NKp46, indicating that the dynamic movements of these receptors are likely important determinants of NK cell responsiveness.

Abstract

Educated natural killer (NK) cells have inhibitory receptors specific for self major histocompatibility complex (MHC) class I molecules and kill cancer cells more efficiently than do NK cells that do not have such receptors (hyporesponsive NK cells). The mechanism behind this functional empowerment through education has so far not been fully described. In addition, distinctive phenotypic markers of educated NK cells at the single-cell level are lacking. We developed a refined version of the image mean square displacement (iMSD) method (called iMSD carpet analysis) and used it in combination with single-particle tracking to characterize the dynamics of the activating receptor NKp46 and the inhibitory receptor Ly49A on resting educated versus hyporesponsive murine NK cells. Most of the NKp46 and Ly49A molecules were restricted to microdomains; however, individual NKp46 molecules resided in these domains for shorter periods and diffused faster on the surface of educated, compared to hyporesponsive, NK cells. In contrast, the movement of Ly49A was more constrained in educated NK cells compared to hyporesponsive NK cells. Either disrupting the actin cytoskeleton or adding cholesterol to the cells prohibited activating signaling, suggesting that the dynamics of receptor movements within the cell membrane are critical for the proper activation of NK cells. The faster and more dynamic movement of NKp46 in educated NK cells may facilitate a swifter response to interactions with target cells.